What qualities do you look for when building successful partnerships?

From my perspective there are many individual parameter. However, the subsequent aspects came to me again and again.

Communitcation:
When discussing a potential partnership, clear and transparent communication helps you to avoid misunderstandings and conflicts. 
Mission:

Be clear, that you share the same goals and values both parties can agree on. This ensures that both parties are working towards the same end goal.

Strengths: 

Partnerships should be built on the premise that both parties bring different strengths to the table. Each partner should be able to contribute their unique skills and knowledge to the partnership.
Committment:

Both partners should demostrate high level of committment. Especially in the early days this will drive your cooperation. 
Compromise:

At the same time the ability to compromise is what makes the partnership work. This means being open to new ideas and suggestions and adapting to changes as needed.

Communication skills are critical. The ability to be transparent, candid and to over-communicate become critical to not only building but also maintaining successful partnerships.

This is a easy one trust and competence these are 2 core building blocks for relationship building. 

I believe that you don't want to build up partnerships, it has to be authentic. I've spoken at customer conferences for companies, but they benefited by having the voice of the customer present because that aided their effort. That had a definite contribution to the renewal conversation. In cases where it didn’t, it was because that partnership did not reflect.

Our head of procurement at a number of companies reiterated feedback to some of the partners, which was, "This does not reflect the partnership that we think we have built." That message reverberated from the AE, right up to the VP of sales, which actually did cause them to take a step back and say, "We have our numbers, but there's no metric here for partnership and customer value. Yousuf and his team have stepped up and this company has stepped up for us in time. And that needs to be reflected." Getting indicators of that dynamic early is important.

When I was at eBay, what I appreciated about the NetApp team as a partner was their transparency in terms of their product roadmap. They gave us visibility into its direction a few years out so that we could actually think about the major investments that we needed to do, whereas most organizations wouldn't even offer that. These traits go a long way towards developing trust and really cementing a partnership.